The interactions of ergot alkaloids and of other drugs with dopamine (DA) and α-adrenergic receptors were investigated. The tested ergot alkaloids inhibit synaptosom-al tyrosine hydroxylase activity and reverse the apomorphine-elicited inhibition of synapto-somal tyrosine hydroxylase activity. Thus, egot alkaloids interact as both agonists and antagonists with the presynaptic DA receptors. Ergot alkaloids also compete effectively for the binding of 3H-DA and 3H-haloperidol to bovine striatal membranes. These results show that these drugs are mixed agonist-antagonists with respect to the postsynaptic DA receptors. To determine the effects of ergot alkaloids and of neuroleptics on the α-adrenergic receptors in the CNS, we have measured their effects on the binding of 3H-dihydroergocryp-tine and 3H-WB-4101 to cerebral cortical membranes. The displacing potencies of the tested ergot alkaloids and of the neuroleptics indicated that they have a high affinity for the α-adrenoreceptors in the CNS. The mechanisms underlying the therapeutic efficacy of mixed agonist-antagonists of DA and α-adrenergic receptors in Parkinson’s disease and in geriatric disorders were considered.